The present invention relates to a method and apparatus for delivering a topical anesthetic solution to the ear canal and tympanic membrane for anesthetizing the ear canal and the tympanic membrane in a manner that is safe, relatively quick, inexpensive, and painless.
Anesthetizing certain regions of the body presents inherent difficulties. In certain instances, anesthetizing procedures can be more expensive, painful, invasive, and/or cumbersome than the simple medical procedures for which the anesthesia is needed. For example, the ear canal is an extremely sensitive structure often requiring local or general anesthesia in order to perform relatively simple procedures, such as removing a foreign body or incising the eardrum to evacuate fluid and place a ventilating tube. It has been estimated that there are more than 1.5 million myringotomies performed in the United States every year, and many are performed on completely anesthetized children. Other simple procedures typically performed on the skin, such as insertion of an intravenous tube, mole removal, or laser removal of skin lesions can require or benefit from the application of a local anesthetic at the site of the procedure.
Use of a general anesthetic raises the cost of the procedure, and requires the presence of many highly skilled medical professionals. In these cases, care shifts by necessity from a physician""s office to an out-patient surgical center or hospital, thus further raising the cost of the procedure.
Conventional topical anesthetics do not penetrate the skin of the ear canal without the use of an iontophoreseis device that requires the placement of electrodes near the ear and the passage of an electrical current therethrough. Topically applied EMLA""s (Eutectic Mixture of Local Anesthetics), typically available in a cream form, are difficult to place in and remove from the ear canal.
Tetracaine (2-dimethylamino-ethyl-p-butylaminobenzoate, CH3(CH2)3NHC6H4COOCH2CH2N(CH3)2) is a known anesthetic agent that is used in various formulations. Tetracaine is available in powder form and is typically dissolved in a solution with a solvent of buffered saline. As an anesthetic, Tetracaine is much more potent than other commonly used anesthetic agents, such as Cocaine or Novocaine, and it is stable at sterilizing temperatures. After application of a Tetracaine-based anesthetic, anesthesia can be effected in about 15 minutes to one hour and can last for up to 1xc2xd-3 hours. On the other hand, Tetracaine is also significantly more toxic than other anesthetics. For this reason, tetracaine is not used internally or in mucosal areas unless at very low dosages. For example, solution concentrations on the order of 0.5% Tetracaine have been used in ophthalmic applications, concentrations of 1 to 2% have been used in the mouth or nose and applied as a spray, and 0.1 to 0.5% solutions have been used in spinal or epidural applications. At such low concentrations, however, even tetracaine-based anesthetics have limited effectiveness in topical applications. Moreover, anesthetic solutions of Tetracaine and saline have poor transdermal effectiveness, except in mucosal tissues.
Presently, a topical anesthetic gel containing tetracaine is commercially available in the United Kingdom from Smith and Nephew Healthcare Ltd. under the trade name Ametop Gel. The gel can be applied topically to the skin where it is purported to prevent needle pain by promoting passive diffusion of a local anesthetic drug through the skin barrier, where it blocks the underlying pain receptors. Also, a topical anesthetic spray containing Tetracaine and indicated for production of anesthesia of accessible mucous membranes is presently available from Cetylite Industries, Inc. under the tradename Cetacaine(copyright).
Ametop Gel is not particularly suited for ear canal applications, because gels are difficult to place in and remove from the ear. Cetacaine(copyright) is effective only on mucosal tissues, such as the mouth and nose.
Carrasco et al. describe a technique for anesthetizing the tympanic membrane using a solution of about 80 mg of tetracaine base dissolved in about 20 drops of isopropyl alcohol. Carrasco, Vincent, N., et al., A Safe, Effective Anesthetic Technique for Outpatient Myringotomy Tube Placement, Laryngoscope 103: January 1993, pp 92-93. A cottonoid is moistened with the solution and is placed on the tympanic membrane for about 15 minutes using an alligator forceps. One potential problem with such a technique, however, is that, because the solvent is alcohol, the solution can evaporate before anesthesia is complete. Furthermore, the moistened cottonoid, being relatively soft and limp, may not maintain sufficient pressure with the tympanic membrane and the walls of the ear canal to properly effect anesthesia.
The need exists, therefore, for a safe, effective, and cost-effective apparatus and method for anesthetizing surface tissues of the body and, in particular, the ear canal and tympanic membrane.
The invention, in one form, is a solution comprising 8-20% tetracaine and 70-80 wt % isopropyl alcohol. A stabilizer and a preservative may be added to the solution.
In another form, the invention is an apparatus for applying a fluid topical anesthetic to the ear canal and tympanic membrane. The apparatus comprises an expandable absorbent applicator, which is maintained in a compressed configuration when in a dry state and which expands when in a fluid-soaked state. An applicator withdrawal tether is attached to the applicator to facilitate withdrawal of the applicator from an ear canal into which the applicator has been inserted. An applicator inserting and soaking device includes an elongated insertion portion defining a fluid conduit therein, a fluid reservoir, and a fluid forcing mechanism for forcing fluid from the reservoir through the conduit. The applicator is releasably secured to a distal end of the insertion portion for inserting the applicator into an ear canal, and fluid can be forced from the reservoir, through the conduit, and out the distal end to soak the applicator.
In yet another form, the invention is a method of anesthetizing the ear canal and the tympanic membrane using a topical anesthetic solution. The method comprises providing an expandable absorbent applicator in a dry, compressed condition, the applicator being constructed and arranged to expand when wetted. An anesthetic solution, comprising Tetracaine dissolved in a solvent, is provided, and the applicator is inserted in a dry, compressed condition or a partially wetted, partially expanded condition into the ear canal and is advanced to a position contacting or adjacent to the tympanic membrane. The entire applicator is wetted with the anesthetic solution to cause the applicator to fully expand, so that an outer surface of the applicator and the anesthetic solution absorbed by the applicator are in contact with the inner walls of the ear canal and the tympanic membrane, and the expanded applicator is left in the ear canal for a period of time sufficient to attain a desired level of anesthetization of the ear canal and tympanic membrane. After the desired level of anesthetization is attained, the applicator is withdrawn from the ear canal.
In yet another form, the invention comprises a set of instruments useful for anesthetizing the ear canal and the tympanic membrane with a topical anesthetic solution. The set comprises an absorbent applicator, an applicator gripping and inserting device, and a fluid injecting device. The applicator is initially in a dry, compressed condition and is constructed and arranged to expand when wetted. The applicator gripping and inserting device is adapted to grip the applicator and insert it into the ear canal therewith. The fluid-injecting device includes a reservoir for containing an amount of topical anesthetic solution and is adapted to inject topical anesthetic solution from the reservoir to the applicator inserted into the ear canal where it is absorbed by the applicator, thereby causing the applicator to expand within the ear canal so that an outer surface of the applicator and the anesthetic solution absorbed by the applicator are in contact with the inner walls of the ear canal and the tympanic membrane.